A typical beverage can is constructed from a can body and a can cover. This disclosure is directed solely to apparatus which stamps the can body.
A known prior art can body forming apparatus has four primary operable components, these being an ironing die, a re-draw sleeve, a ram and a cam/crank. The ironing die has a flat surface and a cylindrical opening therethrough disposed at the surface. The ram is reciprocatingly received through the opening. The clearance between the outer diameter of the ram and the inner diameter of the ironing die opening is commensurate with the thickness of the can body being formed. The re-draw sleeve is a cylinder in coaxial alignment with the ironing die opening and has a diameter larger than the diameter of the opening. The re-draw holds a can material preform on the ironing die surface over the opening prior to the ram forming the can body. The function of the re-draw sleeve is to hold the can material preform tightly against the die, thereby preventing material wrinkling as the ram drives the preform through the die opening. The ram is connected to the cam/crank by a connecting rod for the crank function of the cam/crank. Thus, the ram reciprocates at a frequency determined by the rotational frequency of the cam/crank. The re-draw sleeve is operable from the cam surface of the cam/crank through a push rod arrangement. Conventionally, the cam surface controls the timing of the action of the re-draw sleeve with respect to the position of the ram.
In operation, the cam/crank initially has both the ram and the re-draw sleeve in their full retracted position wherein the ram is removed from the ironing die opening and the re-draw sleeve is removed from the ironing die surface. A can material preform is dropped into place over the opening on the ironing die surface. The preform is usually cup-shaped. The rotation of the cam/crank next causes the re-draw sleeve to engage the inside of the cup-shaped preform and hold it against the ironing die surface. Continuing rotation of the cam/crank thrusts the ram into the preform. As the ram continues into the opening, the can body is formed. After one-half cycle of the crank, the ram is in its fully extended position at which it pushes the newly formed can body out the other side of the ironing die. During the second half of the cam/crank cycle, both the ram and re-draw sleeve are returned to their fully retracted position so that the next can material preform can be positioned to repeat the cycle.
One disadvantage and limitation of the above prior art apparatus is that the pushrod assembly which actuates the re-draw sleeve is off axis with respect to the re-draw sleeve. Because the force of the pushrod assembly is not co-axial with the re-draw sleeve, cam followers need to be incorporated into the apparatus to compensate for the side loads developed on the re-draw sleeve, otherwise the re-draw sleeve will not exert a uniform force along its edge against the can material preform. Accordingly, an increased number of mechanical parts are necessary to handle the side loads developed in the prior art mechanical re-draw sleeve actuator. These additional parts increase complexity and maintenance of the can forming apparatus. Furthermore, because of the intensity of the loads developed, these parts have been found to be failure prone.
These mechanical parts are mostly in the form of linkages which, because of their length and complexity, limit the speed at which the re-draw sleeve can be operated, thus limiting overall system speed. Since the force along the linkages is off axis with respect to the re-draw sleeve, the total force which can be applied thereto is accordingly limited. Excessive force will cause flexure in the linkages thereby limiting the total force the re-draw sleeve can exert on the can material preform. Also, as mentioned hereinabove, this flexure may cause the force at the edge of the re-draw sleeve to be nonuniform.
Thus, the adaptation of the prior art apparatus to other than pure aluminum preforms is difficult. Furthermore, as the linkages wear over time, the total force that the re-draw sleeve can exert against the preform inherently decreases, thereby degrading overall operation of the can forming apparatus. For example, the total speed at which the apparatus can operate degrades, or the force along the edge of the re-draw sleeve on the can preform becomes nonuniform resulting in defective can bodies.